This invention relates to a stimulus for measuring the field of vision of the human eye which is presented to a test subject as a region of the background of a perimeter.
In perimetry measurement, stimuli are used in particular for the early detection of disorders and also for the observation of the changes in said disorders. The stimuli are presented for relatively short periods of time in defined points of the field of vision. The stimuli of the prior art are points of light that appear for brief periods on the surface of the perimeter. Thresholds can be determined by varying the luminance. The stimuli used for this purpose are presented at different luminous intensities and the test subject is required to push a response button when the stimulus is perceived. The stimulus is displayed at predetermined test locations with greater and lesser intensity so that a sensitivity threshold is exceeded one or more times. The threshold is a stimulus intensity (in decibels) at which, after a certain number of presentations, 50% of the presentations are seen. With the stimuli of the prior art, therefore, only the luminance is varied.
An important perimeter test method is used for the early detection of glaucoma. The essential feature is the selective recognition of magnocellular fibers. The detection of such fibers can be used for the early detection of glaucoma. Magnocellular systems have fibers with relatively large diameters, and these fibers age more rapidly than fibers with smaller diameters, which are part of the parvocellular system. With the stimuli of the prior art, it is difficult and very time-consuming to detect magnocellular systems. As mentioned above, however, this capability would be very desirable for the early detection of glaucoma.
The object of the invention is to create a stimulus and a method for the early detection of glaucoma, among other disorders, which makes a more rapid and more reliable test method possible. The method is a method for measuring or testing the perimetry of the field of vision.
The invention teaches a stimulus of the general type described above that has at least two visual characteristics that can be varied for the determination of the threshold. The stimulus claimed by the invention makes possible a test method in which the stimulus can be varied from one test site to another in terms of two characteristics. These two characteristics include, but are not limited to, contrast and resolution. The variation of two characteristics makes possible a more reliable, more rapid and selective detection of magnocellular fibers.
In one embodiment of the invention, a stimulus of the type described above is formed by sine waves. These waves preferably form wave crests and wave troughs that are moved radially outward from a center. The appearance of a stimulus of this type resembles the surface of a liquid after the impact of a drop of fluid on the surface. Radially outward, toward the periphery, the amplitude of the waves becomes smaller and approaches the background. The two characteristics that can be easily and precisely varied with such a stimulus are the amplitude and the distance between the wave crests and the wave troughs. However, the waves can also be moved outward more rapidly or more slowly. Finally, it is also possible to vary the color. Subsequent stimuli can therefore be differentiated in particular with reference to their contrast and/or their resolution. For example, in the presentation of an additional stimulus, the contrast or the resolution can be varied. It is also possible, however, to vary the contrast and the resolution simultaneously. Different cellular systems respond differently to such variations. Such different functions can be diagnosed using the stimuli claimed by the invention.
The method claimed by the invention is characterized by the fact that the stimulus is varied in terms of two visual characteristics during one test. The method is therefore based on the teaching that the stimulus is varied from one test site to another not only in terms of one characteristic, but also in terms of two characteristics. These characteristics are preferably contrast and resolution. An additional characteristic is the speed of movement, for example, the speed at which a wave is moved radially outward from a center. Therefore in one additional conceivable realization, the stimulus is varied with regard to more than two characteristics. With an unchanging luminance, for example, the contrast and/or the resolution and/or the speed of movement can be varied to determine a threshold.